Many operations performed during semiconductor fabrication involve bombarding a wafer workpiece with charged particles to “dope” the workpiece by forming layers or pockets on the workpiece that have a relatively high concentration of a given type of particle. To accomplish this doping, ion beams are created to carry desired particles to a workpiece and impact the surface of the workpiece. The ion beam can be in the form of a pencil beam that is scanned across a workpiece surface or a ribbon beam that has a width slightly larger than the diameter of the workpiece. In the case of the ribbon beam, the beam is often stationary and the workpiece is moved through the beam to effect ion bombardment of the entire workpiece surface.
In order to achieve uniform ion implantation across the surface of the workpiece with a ribbon beam, it is desirable to accurately control the current density of the ribbon beam. Two dimensional current measurement of the ribbon beam is necessary to determine whether the current density is constant throughout the ribbon beam. Presently, a traveling dosimetry cup is utilized in some ion implantation machines that feature a ribbon ion beam. The dosimetry cup is scanned linearly across the ribbon beam to measure current density as a function of location within the beam. While this technique has been used quite successfully in commercially available ion implantation machines, the relatively slow speed of the mechanical motion, which is a translation across the ribbon with acceleration and deceleration at the edges of the ribbon, may slow ion beam setup time.